bk commit into 5.0 tree (konstantin:1.1836)

[konstantin]

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5.0 repository of kostja. When kostja does a push these changes will
be propagated to the main repository and, within 24 hours after the
push, to the public repository.
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ChangeSet
  1.1836 05/04/14 17:47:48 konstantin@stripped +1 -0
  Add a comment to update_ref_and_keys

  sql/sql_select.cc
    1.315 05/04/14 17:47:43 konstantin@stripped +7 -3
    Add a comment to update_ref_and_keys

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User:	konstantin
# Host:	dragonfly.local
# Root:	/media/sda1/mysql/mysql-5.0-root

--- 1.314/sql/sql_select.cc	2005-04-11 01:22:28 -07:00
+++ 1.315/sql/sql_select.cc	2005-04-14 17:47:43 -07:00
@@ -3161,10 +3161,14 @@
   }
 
   /*
-    Special treatment for ft-keys.
-    Remove the following things from KEYUSE:
+    Sort the array of possible keys and remove the following key parts:
     - ref if there is a keypart which is a ref and a const.
-    - keyparts without previous keyparts.
+      (e.g. if there is a key(a,b) and the clause is a=3 and b=7 and b=t2.d,
+      then we skip the key part corresponding to b=t2.d)
+    - keyparts without previous keyparts
+      (e.g. if there is a key(a,b,c) but only b < 5 (or a=2 and c < 3) is
+      used in the query, we drop the partial key parts from consideration).
+    Special treatment for ft-keys.
   */
   if (keyuse->elements)
   {